Default port of mysql is 3306 . To change the default port to custom port , Please follow the below steps :- 

Step 1 : First , use the below command to check the availability of port (port is free or not) .

Command : netstat -tanp|grep 3337

Step 2 : Open the mysql configuration file /etc/my.cnf .

Command :  vi /etc/my.cnf

Step 3 : In my.cnf find the [mysqld] section. Edit the port no. 3306 to 3337(or any) or if you do not find any such line you can add port = 3337 in my.cnf but it should be under the [mysqld] section as shown in the screenshot below .

Press ‘i’ for the insert mode . 

Now save and exit from the file using (backspace) :wq .

Step 4: Restart the mysql service .

Step 5 : To verify the port number of mysql , use the following command :

Command : # netstat -tlpn | grep mysql

Step 6 (Optional): If you have firewalld on your server , then open the required port by the following :

command : # firewall-cmd –permanent –zone=public –add-port=3337/tcp

Step 7 : Login to mysql with custom port using following command : 

Command # mysql -h localhost -u root -p -P 3337

THANK YOU !